The invention relates to a method of manufacturing a display device comprising a display window, a phosphor pattern and a color filter pattern between said display window and said phosphor pattern, the color filter pattern being provided by means of an illumination process.
The invention also relates to a display device comprising a display window, a phosphor pattern and a color filter pattern between the display window and the phosphor pattern.
Color display devices are employed, inter alia, in television receivers and computer monitors.
A color display device of the type mentioned above is known. Said known color display device comprises a phosphor pattern including sub-patterns of phosphor regions luminescing in red, green and blue (hereinafter also referred to as xe2x80x9credxe2x80x9d, xe2x80x9cgreenxe2x80x9d and xe2x80x9cbluexe2x80x9d phosphors), and it further comprises a black matrix. A black matrix layer is a black layer provided with apertures or a system of black stripes on the substrate and (partly) between the phosphor regions of which the phosphor pattern is built up, said black matrix layer improving the contrast of the image displayed. The black matrix is provided with apertures, which accommodate colored layers (also referred to as color filter layers) on which a phosphor region of a corresponding color is deposited. The color filter layer absorbs incident light of wavelengths other than the wavelength of the light emitted by the relevant phosphor. This results in a reduction of the diffuse reflection of incident light and improves the contrast of the image displayed. In addition, the color filter layer (for example a xe2x80x9credxe2x80x9d layer) may absorb a part of the radiation emitted by the xe2x80x9credxe2x80x9d phosphor, i.e. the part having wavelengths outside the red portion of the visible spectrum. This results in an improvement of the color point of the red phosphor. The known color display device has a color filter layer for each of the phosphors (red, green and blue). For clarity, it is noted that xe2x80x9credxe2x80x9d, xe2x80x9cbluexe2x80x9d and xe2x80x9cgreenxe2x80x9d color filter regions have a relatively high transmission for, respectively, red, blue and green light. The color indication of the color filter layers relates to the transmission properties of the filters, not to their color. The color filter layers are customarily provided by means of an illumination process. For this purpose, a photoresist is provided and exposed to (UV) light.
The color filter patterns increase the contrast. It has been found, however, that in known methods and known display devices, the gain in contrast is insufficient.
It is an object of the invention to provide a method by means of which the contrast can be improved, and to provide a display device having an improved contrast.
To achieve this, the method in accordance with the invention is characterized in that a color filter pattern is provided by means of a negative lithography process in which a non-linear photoresist is used.
The color filter layers contain absorbing substances (pigments). Due to the relatively low extinction coefficients of the absorbing substances in the blue color filter pattern, the thickness of this pattern is relatively large. When use is made of a linear negative lithographic photoresist (for example PVA/ADC or PVA/SBQ resists) there is a risk that, for example, blue color filter materials will deposit at positions of green and/or red phosphor elements. Since the blue color filter material absorbs green and red light, this causes the contrast to be reduced. In the known method, the maximum, usable thickness of the blue color filter pattern is approximately 2.0-2.5 micrometer. At a larger thickness, the above problem is aggravated such that the contrast is reduced substantially. The above-mentioned positive effect of the invention also occurs with other color filter patterns.
In the method in accordance with the invention, use is made of a non-linear resist. By virtue thereof, the adhesion of color filter material at positions of phosphor elements of a different color can be precluded more effectively. A further advantage resides in that the thickness of the color filter pattern (no matter which color) exhibits less variation. This has a positive effect on the contrast.
The blue color filter pattern is preferably thicker than 4 micrometer, preferably approximately 6 micrometer (for example in the range between 5 and 7 micrometer).
The invention is also based on the realization that, as a function of the thickness of a color filter pattern, the gain in contrast varies and exhibits an optimum. In the case of a blue color filter pattern, this optimum occurs at a value above 4 micrometer. The display device in accordance with the invention has a blue color filter pattern with a thickness above 4 micrometer, preferably in the range between 5 and 7 micrometer.
In the case of display devices having a red color filter pattern, the thickness of the red color filter pattern preferably ranges between 0.25 and 1.5 micrometer. In this range, a gain in contrast is achieved. Preferably, the thickness of the red color filter pattern ranges between approximately 0.25 and approximately 0.37 micrometer, or between approximately 0.45 and approximately 0.60 micrometer. The gain in contrast exhibits optima at these thicknesses.
The term xe2x80x9cthicknessxe2x80x9d is to be taken to mean within the scope of the invention, the average thickness of the color filter below phosphor elements.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.